Geometric approach to stress reduced intra-flow path shrouds for tuning modal responses in ram air turbine rotors

ABSTRACT

A ram air turbine rotor comprises at least one intra-flow path shroud structure coupled between rotor blades, along a radial position between a support disc and an outer rim. The shroud structure includes shroud sectors each coupled between a respective pair of blades. The sectors each include a first edge adjacent to leading edges of the respective pair of blades, the first edge including a first curved segment, and a second edge adjacent to trailing edges of the respective pair of blades, the second edge including a second curved segment. The curved segments are each partially defined by a respective ellipse having a semi-major axis and a semi-minor axis. The semi-major axis is a portion of a spanwise distance between the respective pair of blades. The semi-minor axis is a portion of an axial distance between the leading edge of one blade and the trailing edge of an adjacent blade.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support. The Government hascertain rights in the invention.

BACKGROUND

Ducted ram air turbine rotors can be exposed to extreme amounts of inletdistortion, due to very constrained space allocations and veryaggressive flight operations. The inlet distortion can excite naturalresonances of vibration modes within the rotor airfoils with enoughenergy to break the rotor. For a robust design, it is necessary todesign the rotor such that a minimum number of vibration modes arewithin the operating range. This is commonly referred to as modeavoidance.

Mode avoidance can be achieved on a practical weight efficient method bythe addition of circumferential shrouds within the flow path. Withtraditional shaped intra-flow path shrouds, the operating stresses inand around the shrouds can become too large to provide proper modeavoidance. In addition, other common tuning approaches, such asthickness redistribution methods, may not yield sufficient amounts oftuning to move the modes out of the operating range.

SUMMARY

A ram air turbine rotor comprises a support rotor disc, and a pluralityof rotor blades coupled to the support rotor disc, the rotor bladesextending radially outward from the support rotor disc, wherein each ofthe rotor blades has a leading edge and a trailing edge. An outer rim iscircumferentially coupled to each of the rotor blades at distal endsthereof. A first intra-flow path shroud structure is coupled betweeneach of the rotor blades along a first radial position between thesupport rotor disc and the outer rim. The first intra-flow path shroudstructure includes a plurality of first shroud sectors, wherein each ofthe first shroud sectors is coupled between a respective pair of therotor blades. The first shroud sectors each include a first shroud edgeadjacent to the leading edges of the respective pair of the rotorblades, with the first shroud edge including a first curved segment, anda second shroud edge adjacent to the trailing edges of the respectivepair of rotor blades, with the second shroud edge including a secondcurved segment. The first and second curved segments are each partiallydefined by a respective ellipse having a semi-major axis and asemi-minor axis. The semi-major axis is a predetermined portion of aspanwise distance along the shroud structure between the respective pairof the rotor blades. The semi-minor axis is a predetermined portion ofan axial distance between the leading edge of one rotor blade and thetrailing edge of an adjacent rotor blade of the respective pair of therotor blades.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure will be apparent to those skilled inthe art from the following description with reference to the drawings.Understanding that the drawings depict only typical embodiments and arenot therefore to be considered limiting in scope, the embodiments willbe described with additional specificity and detail through the use ofthe drawings, in which:

FIG. 1A is an end view of a ram air turbine rotor, from a forwardperspective looking aft, according to one embodiment;

FIG. 1B is a perspective view of a section of the ram air turbine rotorof FIG. 1A;

FIG. 1C is an enlarged perspective view of a section of the ram airturbine rotor of FIGS. 1A and 1B;

FIG. 2 is a graphical representation of parameters defining geometry foran intra-flow path shroud structure of a ram air turbine rotor,according to one example implementation;

FIGS. 3A and 3B are graphical representations of parameters defininggeometry for an intra-flow path shroud structure, according to anotherexample implementation;

FIGS. 4A and 4B are graphical representations of parameters defininggeometry for an intra-flow path shroud structure, according to a furtherexample implementation;

FIGS. 5A and 5B are graphical representations of parameters defininggeometry for an intra-flow path shroud structure, according to anotherexample implementation;

FIGS. 6A and 6B are graphical representations of parameters defininggeometry for an intra-flow path shroud structure, according to analternative implementation; and

FIG. 7 is a Campbell diagram showing the modal benefits of using anintra-flow path shroud in a ram air turbine rotor.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, in which is shown by way of illustration variousexemplary embodiments. It is to be understood that other embodiments maybe utilized. The following detailed description is, therefore, not to betaken in a limiting sense.

A geometric approach is described herein that provides stress reducedintra-flow path shrouds for tuning modal responses in ram air turbinerotors. The intra-flow path shrouds are designed to have minimal stressconcentration by the strategic placement of scallop-shaped sections inacute corners of a shroud-to-blade interface. This configurationprovides enhanced mode avoidance, which gives ram air turbine rotors amore robust design.

The present approach maintains the mode avoidance capabilities ofsimpler midspan shroud designs, and produces minimal aerodynamic impactfor the ram air turbine rotor. Additionally, modal tuning for modeavoidance is achieved without the addition of significant weight to ramair turbines.

Further, the present approach increases the flight envelope in which ramair turbine rotors are not subject to harmful vibrations during flight.These harmful vibrations are avoided by tuning modes out of theoperating range of the ram air turbine rotor.

In a method of making the present ram air turbine rotors, the intra-flowpath shrouds are formed to have scallop-shaped sections in acute cornersof the shroud-to-blade interface. The scallop shapes are created such asto be viewed from the outboard looking inboard radial direction, andminimize the circumferential stress concentration at the interface. Theshrouds are also shaped in the flow direction to have minimalinterference with aerodynamic performance. The shroud structures areformed in one or more bands circumferentially around a middle portion ofthe air flow path in the ram air turbine rotors.

Further details of various embodiments are described hereafter withreference to the drawings.

FIGS. 1A-1C illustrate a ram air turbine rotor 100, according to oneembodiment. Generally, ram air turbine rotor 100 includes a supportrotor disc 110, and a plurality of rotor blades 120 coupled to rotordisc 110. A first intra-flow path shroud structure 130 is coupledbetween rotor blades 120 at a first radial position. Optionally, asshown, a second intra-flow path shroud structure 140 is coupled betweenrotor blades 120 at a second radial position that is further away fromrotor disc 110 than the first radial position. An outer rim 150 iscircumferentially coupled to rotor blades 120 at distal ends thereof.

The rotor disc 110 can be annular-shaped and extends continuously abouta centerline axis 115 (FIG. 1A). The rotor disc 110 is configured to bemounted on a shaft for rotation about centerline axis 115. The rotorblades 120 are mounted to a circumferential region 112 of rotor disc 110and project outwardly along a radial axis 117. In one embodiment, rotorblades 120 are evenly spaced about circumferential region 112 of rotordisc 110. In other embodiments, rotor blades 120 can be unevenly spacedabout circumferential region 112.

Each of rotor blades 120 includes a first face 122 and an opposingsecond face 123. The first face 122 and second face 123 cooperate todefine a blade airfoil shape. In a chordwise direction, each first face122 and second face 123 are joined at a leading edge 125 and a trailingedge 126 along a radial length of rotor blades 120. As used herein, theterm “chordwise” refers to a direction along the blade between theleading edge and the trailing edge.

The rotor blades 120 can have a complex, three-dimensional curvature.For example, rotor blades 120 can have a predetermined amount of bladetwist angle, sweep, and other curvature. It will be appreciated thatrotor blades 120 may have alternate configurations or arrangementswithout departing from the scope of the present disclosure.

As shown in FIGS. 1B and 1C, shroud structure 130 includes a pluralityof shroud sectors 132. Each shroud sector 132 is coupled between arespective pair of rotor blades 120 at shroud-to-blade interfaces 134.Each shroud sector 132 includes a first shroud edge 135 adjacent toleading edge 125 of the respective pair of rotor blades 120, and asecond shroud edge 136 adjacent to trailing edge 126 of the respectivepair of blades 120. The first shroud edge 135 includes a first curvedsegment 137, and second shroud edge 136 includes a second curved segment138 (FIG. 1C).

Similarly, shroud structure 140 includes a plurality of shroud sectors142. Each shroud sector 142 is coupled between a respective pair ofrotor blades 120 at shroud-to-blade interfaces 144. Each shroud sector142 includes a first shroud edge 145 adjacent to leading edge 125 of therespective pair of rotor blades 120, and a second shroud edge 146adjacent to trailing edge 126 of the respective pair of blades 120. Thefirst shroud edge 145 includes a first curved segment 147, and secondshroud edge 146 includes a second curved segment 148 (FIG. 1C).

As described in further detail hereafter, the curved segments of theshroud edges are each partially defined by a semi-major axis andsemi-minor axis of an ellipse. The semi-major axis is a predeterminedportion of a spanwise distance along the shroud structure between arespective pair of the rotor blades. The semi-minor axis is apredetermined portion of an axial distance between the leading edge ofone rotor blade and the trailing edge of an adjacent rotor blade of therespective pair of the rotor blades. In some embodiments, the curvedsegments are also each partially defined by a circle adjacent to theellipse to form a blend region, with the circle having a predetermineddiameter.

For example, the semi-major axis can be about 10% to about 40% of aspanwise distance along the shroud structure between a respective pairof adjacent blades, the semi-minor axis can be about 10% to about 40% ofan axial distance between the leading edge of one blade and the trailingedge of an adjacent blade. In some embodiments, the curved segments arealso each partially defined by a circle adjacent to the ellipse to formthe blend region, with the circle having a diameter that is 0% to about25% of the axial distance between the leading edge of one blade and thetrailing edge of an adjacent blade.

FIG. 2 is a graphical representation of parameters defining geometry foran intra-flow path shroud structure of a ram air turbine rotor,according to one example implementation. In this example, the shroudstructure is represented from a radial point of view looking inboard,with respect to sector length vs. axial length. As shown in FIG. 2 ,curve 210 represents a leading edge (LE) profile of the shroudstructure, curve 212 represents a trailing edge (TE) profile of theshroud structure, and curve 214 represents a center line of the shroudstructure. The lines 220 represent the blade chord located between eachsector of the shroud structure. The curve 224 represents a “forreference” line, which is used to ensure that there are no abruptchanges in axial thickness of the shroud structure (ratio to max crosssection—1)

The axial distance includes a sector axial distance (H_(s)),representing the axial distance from the leading edge of one blade tothe trailing edge of an adjacent blade, taking into account the twistangle between the blades, which changes the total axial distance fromthe leading edge to the trailing edge of the adjacent blade. The sectoraxial distance H_(s) is defined by the following expression:H _(s) =C*cos(ψ)

-   -   where    -   ψ=Blade Twist Angle, and    -   C=Blade Chord Length.

The spanwise distance along the shroud structure includes a sectorspanwise distance (D_(s)) along the shroud structure, which representsthe angular gap between two coincident points, such as the distance fromthe leading edge of one blade to the leading edge of an adjacent blade,taking into account the wheel radius for a midspan profile and thenumber of blades. The sector spanwise distance D_(s) along the shroudstructure is defined by the following expression:

$D_{s} = {R*\frac{2\pi}{N}}$

where

-   -   R=Wheel Radius For Midspan Profile, and    -   N=Number of Blades.

As shown in FIG. 2 , portions of curve 210 (LE profile) and curve 212(TE profile) are defined by a semi-major axis (a) and semi-minor axis(b) of respective ellipses 230 and 232. Also, the leading edge of theblade chord adjacent to ellipse 230 is defined by a circle 234 with adiameter D_(c) to form a blend region. Similarly, the trailing edge ofthe blade chord adjacent to ellipse 232 is defined by a circle 236 witha diameter D_(c) to form a blend region. A tangent point between ellipse230 and circle 234 leads to a straight line drawn to a tangent pointbetween ellipse 232 and circle 236.

In various embodiments the ellipse and circle can be defined by thefollowing range expressions:0.1D_(s)≤a≤0.4D_(s)0.1H_(s)≤b≤0.4H_(s)0≤D_(c)≤0.25H_(s)

where

-   -   a=Ellipse Semi Major Axis,    -   b=Ellipse Semi Minor Axis, and    -   D_(c)=Circle Diameter.

In other words, the semi-major axis (a) of the ellipse can be about 10%to about 40% of the sector spanwise distance D_(s) along the shroudstructure, the semi-minor axis (b) of the ellipse can be about 10% toabout 40% of the sector axial distance H_(s), and the circle diameter(D_(c)) can be 0% to about 25% of the sector axial distance H_(s).

In the example shown in FIG. 2 , the following values for H_(s) andD_(s) were used:

-   -   H_(s)=0.6428    -   D_(s)=1.1781.

FIGS. 3A and 3B are graphical representations of parameters defininggeometry for an intra-flow path shroud structure, according to anotherexample implementation. In this example, the shroud structure is againrepresented from a radial point of view looking inboard, with respect tosector length vs. axial length. In addition, the following values forthe sector axial distance H_(s) and the sector spanwise distance D_(s)along the shroud structure, were again used:

-   -   H_(s)=0.6428    -   D_(s)=1.1781.

In this example, the minimum values were used based on the above rangeexpressions (FIG. 2 ) for the semi-major axis (a_(min)) and semi-minoraxis (b_(min)) of an ellipse, and a circle diameter (D_(c,min)). Thus,the semi-major axis was computed as 0.1D_(s), the semi-minor axis wascomputed as 0.1H_(s), and the circle diameter was 0% of H_(s), using theabove values for H_(s) and D_(s), which resulted in the followingvalues:

-   -   a_(min)=0.11781    -   b_(min)=0.06428    -   D_(c,min)=0.

The above values were used to generate the shroud geometry shown inFIGS. 3A and 3B, including a curve 310 representing the LE profile ofthe shroud structure, and a curve 312 representing the TE profile of theshroud structure. A curve 314 represents a center line of the shroudstructure. The lines 320 represent the blade chord located between eachsector of the shroud structure. The curve 324 represents a “forreference” line, which is used to ensure that there are no abruptchanges in axial thickness of the shroud structure (ratio to max crosssection—1).

As shown in FIG. 3B, portions of curve 310 (LE profile) and curve 312(TE profile) are defined by respective ellipses 330 and 332, to producethe scalloped profile of the shroud structure. Also, the leading edge ofthe blade chord adjacent to ellipse 330 has a sharp edge 333, as thereis no blend region defined by a circle. Similarly, the trailing edge ofthe blade chord adjacent to ellipse 332 has a sharp edge 335, as againthere is no blend region.

FIGS. 4A and 4B are graphical representations of parameters defininggeometry for the intra-flow path shroud structure, according to afurther example implementation. In this example, the shroud structure isagain represented from a radial point of view looking inboard, withrespect to sector length vs. axial length. In addition, the followingvalues for the sector axial distance H_(s) and the sector spanwisedistance D_(s) along the shroud structure were again used:

-   -   H_(s)=0.6428    -   D_(s)=1.1781.

In this example, the maximum values were used based on the above rangeexpressions (FIG. 2 ) for the semi-major axis and semi-minor axis of anellipse, and the circle diameter of a blend region. Thus, the semi-majoraxis (a_(max)) was computed as 0.4D_(s), the semi-minor axis (b_(max))was computed as 0.4H_(s), and the circle diameter (D_(c,max)) wascomputed as 0.25H_(s), using the above values for H_(s) and D_(s), whichresulted in the following values:

-   -   a_(max)=0.47124    -   b_(max)=0.25712    -   D_(c,max)=0.1607

The above values were used to generate the shroud geometry shown inFIGS. 4A and 4B, including a curve 410 representing the LE profile ofthe shroud structure, and a curve 412 representing the TE profile of theshroud structure. A curve 414 represents a center line of the shroudstructure. The lines 420 represent the blade chord located between eachsector of the shroud structure. The curve 424 represents a “forreference” line, which is used to ensure that there are no abruptchanges in axial thickness of the shroud structure (ratio to max crosssection—1).

As shown in FIG. 4B, portions of curve 410 (LE profile) and curve 412(TE profile) are defined by respective ellipses 430 and 432, to producethe scalloped profile of the shroud structure. Also, the leading edge ofthe blade chord adjacent to ellipse 430 is defined by a circle 440 toform a blend region 442. Likewise, the trailing edge of the blade chordadjacent to ellipse 432 is defined by a circle 444 to form a blendregion 446.

FIGS. 5A and 5B are graphical representations of parameters defininggeometry for the intra-flow path shroud structure, according to anotherexample implementation. In this example, the shroud structure is againrepresented from a radially point of view looking inboard, with respectto sector length vs. axial length. In addition, the following values forthe sector axial distance H_(s) and the sector spanwise distance D_(s)along the shroud structure, were again used:

-   -   H_(s)=0.6428    -   D_(s)=1.1781.

In this example, nominal values were used based on the above rangeexpressions (FIG. 2 ) for the semi-major axis and semi-minor axis of anellipse, and the circle diameter of a blend region. Thus, the semi-majoraxis (a_(nom)) was computed as 0.25D_(s), the semi-minor axis (b_(nom))was computed as 0.25H_(s), and the circle diameter (D_(c, nom)) wascomputed as 0.125H_(s), using the above values for H_(s) and D_(s),which resulted in the following values:

-   -   a_(nom)=0.294525    -   b_(nom)=0.1607    -   D_(c,nom)=0.08035

The above values were used to generate the shroud geometry shown inFIGS. 5A and 5B, including a curve 510 representing the LE profile ofthe shroud structure, and a curve 512 representing the TE profile of theshroud structure. A curve 514 represents a center line of the shroudstructure. The lines 520 represent the blade chord located between eachsector of the shroud structure. The curve 524 represents a “forreference” line, which is used to ensure that there are no abruptchanges in axial thickness of the shroud structure (ratio to max crosssection—1).

As shown in FIG. 5B, portions of curve 510 (LE profile) and curve 512(TE profile) are defined by respective ellipses 530 and 532, to producethe scalloped profile of the shroud structure. Also, the leading edge ofthe blade chord adjacent to ellipse 530 is defined by a circle 540 toform a blend region 542. Likewise, the trailing edge of the blade chordadjacent to ellipse 532 is defined by a circle 544 to form a blendregion 546.

FIGS. 6A and 6B are graphical representations of parameters defininggeometry for the intra-flow path shroud structure, according to analternative implementation. In this example, the shroud structure isagain represented from a radial point of view looking inboard, withrespect to sector length vs. axial length. In addition, the followingvalues for the sector axial distance H_(s) and the sector spanwisedistance D_(s) along the shroud structure, were used:

-   -   H_(s)=0.7456    -   D_(s)=1.0622

In this example, values were used based on the above range expressions(FIG. 2 ) for the semi-major axis and semi-minor axis of an ellipse, andthe circle diameter of a blend region. Thus, the semi-major axis (a) wascomputed as 0.282D_(s), the semi-minor axis (b) was computed as0.2012H_(s) and the circle diameter D_(c) was computed as 0.2682H_(s),using the above values for H_(s) and D_(s), which resulted in thefollowing values:

-   -   a=0.3    -   b=0.15    -   D_(c)=0.2

The above values were used to generate the shroud geometry shown inFIGS. 6A and 6B, including a curve 610 representing the LE profile ofthe shroud structure, and a curve 612 representing the TE profile of theshroud structure. A curve 614 represents a center line of the shroudstructure. The lines 620 represent the blade chord located between eachsector of the shroud structure. The curve 624 represents a “forreference” line, which is used to ensure that there are no abruptchanges in axial thickness of the shroud structure (ratio to max crosssection—1).

As shown in FIG. 6B, portions of curve 610 (LE profile) and curve 612(TE profile) are defined by respective ellipses 630 and 632, to producethe scalloped profile of the shroud structure. Also, the leading edge ofthe blade chord adjacent to ellipse 630 is defined by a circle 640 toform a blend region 642. Likewise, the trailing edge of the blade chordadjacent to ellipse 632 is defined by a circle 644 to form a blendregion 646.

FIG. 7 is a Campbell diagram showing the modal benefits of using theintra-flow path shroud in a ram air turbine rotor. The diagram plots theoperating revolutions per minute (RPM) percentage of a ram air turbinerotor full speed, with respect to the resonance frequency percentage.The diagonal lines 702, 704, and 706 respectively represent excitationsources A, B, and C. The horizontal lines 710 and 712 are typicalresonance modes, respectively without the intra-flow path shroud added(710), and with the shroud added (712).

As shown in FIG. 7 , before the present shroud band is added,potentially harmful crossings of the excitation sources can occur in theoperating range of the ram air turbine rotor. After the intra-flow pathshroud is added, potentially harmful crossings of the excitation sourcesare eliminated. The increased stiffness provided by the intra-flow pathshroud drives the resonance frequency higher, so that the excitationsources do not cross the resonance mode (712) during the operatingrange. It should be noted that the resonance frequency percent changefrom 20 to 80 for the resonance modes shown in FIG. 7 is only exemplary,as such a change provided by the intra-flow path shroud can be greateror less that this amount.

EXAMPLE EMBODIMENTS

Example 1 includes a ram air turbine rotor, comprising a support rotordisc; a plurality of rotor blades coupled to the support rotor disc, therotor blades extending radially outward from the support rotor disc,wherein each of the rotor blades have a leading edge and a trailingedge; an outer rim circumferentially coupled to each of the rotor bladesat distal ends thereof; and a first intra-flow path shroud structurecoupled between each of the rotor blades along a first radial positionbetween the support rotor disc and the outer rim, the first intra-flowpath shroud structure including a plurality of first shroud sectors,wherein each of the first shroud sectors is coupled between a respectivepair of the rotor blades, the first shroud sectors each including: afirst shroud edge adjacent to the leading edges of the respective pairof the rotor blades, the first shroud edge including a first curvedsegment; and a second shroud edge adjacent to the trailing edges of therespective pair of rotor blades, the second shroud edge including asecond curved segment; wherein the first and second curved segments areeach partially defined by a respective ellipse having a semi-major axisand a semi-minor axis; wherein the semi-major axis is a predeterminedportion of a spanwise distance along the shroud structure between therespective pair of the rotor blades; wherein the semi-minor axis is apredetermined portion of an axial distance between the leading edge ofone rotor blade and the trailing edge of an adjacent rotor blade of therespective pair of the rotor blades.

Example 2 includes the ram air turbine rotor of Example 1, wherein thesupport rotor disc is an annular-shaped structure around a centerlineaxis, the support rotor disc configured to be mounted on a shaft forrotation about the centerline axis.

Example 3 includes the ram air turbine rotor of any of Examples 1-2,wherein the rotor blades are spaced about a circumferential region ofthe support rotor disc.

Example 4 includes the ram air turbine rotor of any of Examples 1-3,wherein: the predetermined portion of the spanwise distance along theshroud structure of the semi-major axis of each ellipse is about 10% toabout 40% of the spanwise distance along the shroud structure betweenthe respective pair of the rotor blades; and the predetermined portionof the axial distance of the semi-minor axis of each ellipse is about10% to about 40% of the axial distance between the leading edge of onerotor blade and the trailing edge of the adjacent rotor blade of therespective pair of the rotor blades.

Example 5 includes the ram air turbine rotor of any of Examples 1-4,wherein the spanwise distance along the shroud structure comprises asector spanwise distance (A), which represents an angular gap betweentwo coincident points, including a distance from a leading edge of oneblade to a leading edge of an adjacent blade, taking into account awheel radius for a midspan profile and number of blades, wherein thesector spanwise distance is defined by the expression:

$D_{s} = {R*\frac{2\pi}{N}}$

where

-   -   R=Wheel Radius For Midspan Profile, and    -   N=Number of Blades.

Example 6 includes the ram air turbine rotor of any of Examples 1-5,wherein the axial distance comprises a sector axial distance (H_(s)),which represents a distance from the leading edge of one blade to thetrailing edge of an adjacent blade, taking into account a twist anglebetween the blades, wherein the sector axial distance is defined by theexpression:H _(s) =C*cos(ψ)

where

-   -   ψ=Blade Twist Angle, and    -   C=Blade Chord Length.

Example 7 includes the ram air turbine rotor of any of Examples1-6,wherein the first and second curved segments are each furtherdefined by a respective circle having a predetermined diameter, eachcircle adjacent to each ellipse.

Example 8 includes the ram air turbine rotor of Example 7, wherein thepredetermined diameter of each circle is between 0% to about 25% of theaxial distance.

Example 9 includes the ram air turbine rotor of any of Examples 1-8,wherein the first and second curved segments each have a scallopedprofile defined by each respective ellipse.

Example 10 includes the ram air turbine rotor of any of Examples 1-9,further comprising: at least a second intra-flow path shroud structurecoupled between each of the rotor blades along a second radial positionbetween the support rotor disc and the outer rim, the second intra-flowpath shroud structure including a plurality of second shroud sectors,wherein each of the second shroud sectors is coupled between arespective pair of the rotor blades.

Example 11 includes the ram air turbine rotor of Example 10, wherein thesecond shroud sectors each include: a first shroud edge adjacent to theleading edges of the respective pair of the rotor blades, the firstshroud edge including a first curved segment; and a second shroud edgeadjacent to the trailing edges of the respective pair of rotor blades,the second shroud edge including a second curved segment; wherein thefirst and second curved segments of each second shroud sector arepartially defined by an ellipse having a semi-major axis and asemi-minor axis; wherein the semi-major axis of each second shroudsector is a predetermined portion of a spanwise distance along thesecond intra-flow path shroud structure between the respective pair ofthe rotor blades; wherein the semi-minor axis of each second shroudsector is a predetermined portion of an axial distance between theleading edge of one rotor blade and the trailing edge of an adjacentrotor blade of the respective pair of the rotor blades.

Example 12 includes the ram air turbine rotor of Example 11, wherein thefirst and second curved segments of each second shroud sector arefurther defined by a respective circle having a predetermined diameter,each circle adjacent to the ellipse of each second shroud sector.

Example 13 includes the ram air turbine rotor of any of Examples 1-12,wherein the intra-flow path shroud structures substantially eliminateharmful crossings of one or more excitation sources with a resonancemode, by increasing a resonance frequency of the ram air turbine rotorduring operation.

Example 14 includes a method of tuning modal responses in a ram airturbine rotor, the method comprising: forming at least a firstintra-flow path shroud structure between a plurality of rotor blades atleast at a first radial position in the ram air turbine rotor, the firstintra-flow path shroud structure formed to include a plurality of firstshroud sectors coupled between a respective pair of rotor blades atfirst shroud-to-blade interfaces; and forming the first shroud sectorswith first scallop-shaped sections in acute corners of the firstshroud-to-blade interfaces, the first scallop-shaped sections configuredto minimize a circumferential stress concentration at the firstshroud-to-blade interfaces; wherein the first intra-flow path shroudstructure substantially eliminates harmful crossings of one or moreexcitation sources with a resonance mode, by increasing a resonancefrequency of the ram air turbine rotor during operation.

Example 15 includes the method of Example 14, wherein the firstscallop-shaped sections are each partially defined by a respectiveellipse having a semi-major axis and a semi-minor axis; wherein thesemi-major axis is a predetermined portion of a spanwise distance alongthe shroud structure between the respective pair of the rotor blades;wherein the semi-minor axis is a predetermined portion of an axialdistance between the leading edge of one rotor blade and the trailingedge of an adjacent rotor blade of the respective pair of the rotorblades.

Example 16 includes the method of Example 15, wherein the predeterminedportion of the spanwise distance along the shroud structure of thesemi-major axis of each ellipse is about 10% to about 40% of thespanwise distance along the shroud structure between the respective pairof the rotor blades; and the predetermined portion of the axial distanceof the semi-minor axis of each ellipse is about 10% to about 40% of theaxial distance between the leading edge of one rotor blade and thetrailing edge of the adjacent rotor blade of the respective pair of therotor blades.

Example 17 includes the method of any of Examples 15-16, wherein thefirst scallop-shaped sections are each further defined by a respectivecircle having a predetermined diameter, each circle adjacent to eachellipse.

Example 18 includes the method of Example 17, wherein the predetermineddiameter of each circle is between 0% to about 25% of the axialdistance.

Example 19 includes the method of any of Examples 14-18, furthercomprising: forming one or more additional intra-flow path shroudstructures circumferentially between a plurality of rotor blades at oneor more additional radial positions in the ram air turbine rotor, theone or more additional intra-flow path shroud structures formed toinclude a plurality of additional shroud sectors coupled between arespective pair of rotor blades at additional shroud-to-bladeinterfaces; and forming the additional shroud sectors with additionalscallop-shaped sections in acute corners of the additionalshroud-to-blade interfaces, the additional scallop-shaped sectionsconfigured to minimize a circumferential stress concentration at theadditional shroud-to-blade interfaces.

Example 20 includes the method of Example 19, wherein the one or moreadditional intra-flow path shroud structures eliminate harmful crossingsof one or more excitation sources with the resonance mode, by increasingthe resonance frequency of the ram air turbine rotor during operation.

From the foregoing, it will be appreciated that, although specificembodiments have been described herein for purposes of illustration,various modifications may be made without deviating from the scope ofthe disclosure. Thus, the described embodiments are to be considered inall respects only as illustrative and not restrictive. In addition, allchanges that come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A ram air turbine rotor, comprising: a supportrotor disc; a plurality of rotor blades coupled to the support rotordisc, the rotor blades extending radially outward from the support rotordisc, wherein each of the rotor blades have a leading edge and atrailing edge; an outer rim circumferentially coupled to each of therotor blades at distal ends thereof; and a first intra-flow path shroudstructure coupled between each of the rotor blades along a first radialposition between the support rotor disc and the outer rim, the firstintra-flow path shroud structure including a plurality of first shroudsectors, wherein each of the first shroud sectors is coupled between arespective pair of the rotor blades, the first shroud sectors eachincluding: a first shroud edge adjacent to the leading edges of therespective pair of the rotor blades, the first shroud edge including afirst curved segment; and a second shroud edge adjacent to the trailingedges of the respective pair of rotor blades, the second shroud edgeincluding a second curved segment; wherein the first and second curvedsegments are each partially defined by a respective ellipse having asemi-major axis and a semi-minor axis; wherein the semi-major axis is apredetermined portion of a spanwise distance along the shroud structurebetween the respective pair of the rotor blades; wherein the semi-minoraxis is a predetermined portion of an axial distance between the leadingedge of one rotor blade and the trailing edge of an adjacent rotor bladeof the respective pair of the rotor blades.
 2. The ram air turbine rotorof claim 1, wherein the support rotor disc is an annular-shapedstructure around a centerline axis, the support rotor disc configured tobe mounted on a shaft for rotation about the centerline axis.
 3. The ramair turbine rotor of claim 1, wherein the rotor blades are spaced abouta circumferential region of the support rotor disc.
 4. The ram airturbine rotor of claim 1, wherein: the predetermined portion of thespanwise distance along the shroud structure of the semi-major axis ofeach ellipse is about 10% to about 40% of the spanwise distance alongthe shroud structure between the respective pair of the rotor blades;and the predetermined portion of the axial distance of the semi-minoraxis of each ellipse is about 10% to about 40% of the axial distancebetween the leading edge of one rotor blade and the trailing edge of theadjacent rotor blade of the respective pair of the rotor blades.
 5. Theram air turbine rotor of claim 1, wherein the spanwise distance alongthe shroud structure comprises a sector spanwise distance (D_(s)), whichrepresents an angular gap between two coincident points, including adistance from a leading edge of one blade to a leading edge of anadjacent blade, taking into account a wheel radius for a midspan profileand number of blades, wherein the sector spanwise distance is defined bythe expression: $D_{s} = {R*\frac{2\pi}{N}}$ where R=Wheel Radius ForMidspan Profile, and N=Number of Blades.
 6. The ram air turbine rotor ofclaim 1, wherein the axial distance comprises a sector axial distance(H_(s)), which represents a distance from the leading edge of one bladeto the trailing edge of an adjacent blade, taking into account a twistangle between the blades, wherein the sector axial distance is definedby the expression:H _(s) =C*cos(ψ) where ψ=Blade Twist Angle, and C=Blade Chord Length. 7.The ram air turbine rotor of claim 1, wherein the first and secondcurved segments are each further defined by a respective circle having apredetermined diameter, each circle adjacent to each ellipse.
 8. The ramair turbine rotor of claim 7, wherein the predetermined diameter of eachcircle is between 0% to about 25% of the axial distance.
 9. The ram airturbine rotor of claim 1, wherein the first and second curved segmentseach have a scalloped profile defined by each respective ellipse. 10.The ram air turbine rotor of claim 1, further comprising: at least asecond intra-flow path shroud structure coupled between each of therotor blades along a second radial position between the support rotordisc and the outer rim, the second intra-flow path shroud structureincluding a plurality of second shroud sectors, wherein each of thesecond shroud sectors is coupled between a respective pair of the rotorblades.
 11. The ram air turbine rotor of claim 10, wherein the secondshroud sectors each include: a first shroud edge adjacent to the leadingedges of the respective pair of the rotor blades, the first shroud edgeincluding a first curved segment; and a second shroud edge adjacent tothe trailing edges of the respective pair of rotor blades, the secondshroud edge including a second curved segment; wherein the first andsecond curved segments of each second shroud sector are partiallydefined by an ellipse having a semi-major axis and a semi-minor axis;wherein the semi-major axis of each second shroud sector is apredetermined portion of a spanwise distance along the second intra-flowpath shroud structure between the respective pair of the rotor blades;wherein the semi-minor axis of each second shroud sector is apredetermined portion of an axial distance between the leading edge ofone rotor blade and the trailing edge of an adjacent rotor blade of therespective pair of the rotor blades.
 12. The ram air turbine rotor ofclaim 11, wherein the first and second curved segments of each secondshroud sector are further defined by a respective circle having apredetermined diameter, each circle adjacent to the ellipse of eachsecond shroud sector.
 13. The ram air turbine rotor of claim 1, whereinthe intra-flow path shroud structure substantially eliminates harmfulcrossings of one or more excitation sources with a resonance mode, byincreasing a resonance frequency of the ram air turbine rotor duringoperation.